Thrombin is a proteolytic enzyme formed from prothrombinin plasma during the clotting process.
Thrombin is widely used in clinical applications as a coagulation factor to staunch bleeding of wounds by conversion of fibrinogen to fibrin. It is a common component of surgical dressings, and has been used in combination with fibrinogen and other coagulation proteins in two-component hemostatic systems such as fibrin glues, adhesives, and sealants.
It is known to lyophilize a solution of thrombin to produce a solid thrombin composition prior to storage, in order to reduce protein degradation, wherein the solid thrombin composition may be reconstituted prior to use. Lyophilization typically refers to the process of freezing a mixture and then reducing the concentration of water e.g. by sublimation to levels which do not support biological or chemical reactions. The porous and spongy solid material resulting from the lyophilization process is referred to as a cake. It is desirable for such solid thrombin compositions to have low water content (e.g. less than about 3%), to retain structural and functional stability for long periods), preferably at room temperature, and to retain a high percentage of thrombin activity upon reconstitution as compared to the activity of thrombin in the solution prior to lyophilization.
Examples of background art thrombin solutions are described in EP 813598B1; U.S. Pat. Nos. 5,605,884; 4,877,608; US 2010/0074865; U.S. Pat. No. 5,733,873; EP 1766003; and US 2010/0168018. The background art thrombin solutions vary considerably in the number and types of excipients present, and in the concentrations of the individual excipients.
Cryoprotectants or stabilizers are commonly used in thrombin solutions to protect the thrombin from denaturation or activity loss due to freezing stress, to stabilize the protein in subsequent production steps, and to extend the shelf life. Examples of cryoprotectants include saccharides such as sucrose, lactose, and trehalose; sugar alcohols such as mannitol; and surfactants such as polyethylene glycol, TritonX-100, TWEEN-20, and TWEEN-80. Besides functioning as stabilizers, mannitol and sucrose (to a lesser degree) are also used as bulking agents which help to provide a cake having a strong physical structure. Use of bulking agents is especially important for formulation with a low solid material content (per volume).
Human Serum Albumin (HSA) is also widely used in biopharmaceutical formulations as a stabilizing and bulking agent (H. R. Constantino, M. J. Pikal: Lyophilization of Biopharmaceuticals, Springer, 2004).
EP 813598B1 discloses a simple thrombin formulation for lyophilization, containing 40 mM gluconic acid, 20 mM tri-sodium citrate and 150 mM NaCl; U.S. Pat. Nos. 5,605,884 and 4,877,608 disclose formulations containing up to 10% saccharides such as sucrose, mannitol or maltose; US 2010/0074865 discloses formulation containing 5.7% lactose, 3.1% trehalose and 0.001% TWEEN-80; and U.S. Pat. No. 5,733,873 discloses formulations including 0.001-0.025% polysorbate 80 (TWEEN-80) with or without 0.1% PEG 4000 and 2% mannitol.
Sodium chloride (NaCl) is commonly used for reducing protein precipitation and aggregation during lyophilization of biopharmaceutical formulations. However, EP 1766003 discloses that NaCl can be problematic because it lowers the glass transition temperature, thereby necessitating a low temperature of primary drying and a prolonged drying cycle time. Also, US 2010/0168018 discloses a formulation without NaCl, or with NaCl present in trace amounts.
Methods of lyophilization of such known thrombin solutions are frequently of a very long duration, which increases the cost of the process and/or result in solid thrombin compositions having a relatively high water content and/or which retain a relatively low percentage of thrombin activity upon reconstitution, as compared to the thrombin activity in the solution prior to lyophilization.